Image processing apparatus, image processing method, storage medium, and image forming apparatus

ABSTRACT

Disclosed is an image processing apparatus including: a derivation unit configured to derive a target luminance characteristic based on a viewing condition of an image and a print luminance characteristic predicted based a reflection characteristic corresponding to data thereon; a unit configured to generate print image data on an image by converting input image data by using a tone conversion characteristic that is set based on these characteristics, in which the derivation unit derives, in a case where a reproduction range of an illumination intensity in the print luminance characteristic is different, the target luminance characteristic so that a liner area of an output luminance in a case where the reproduction range is relatively large becomes large.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of International Patent ApplicationNo. PCT/JP2018/038589, filed Oct. 17, 2018, which claims the benefit ofJapanese Patent Application No. 2017-221969, filed Nov. 17, 2017, bothof which are hereby incorporated by reference herein in their entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present disclosure relates to a technique for generating an image inwhich a visual change depending on the viewing environment issuppressed.

Background Art

Conventionally, image forming apparatuses prevail, such as a digitalcopy machine and a printer, using a variety of printing methods, such asink jet, electrophotography, and thermal transfer. Further, it is knownthat the visual density (color) of a printed material produced by usingthese image forming apparatuses changes depending on the viewingenvironment. Here, as one viewing environment, for example, there is anillumination intensity of illumination installed in the viewingenvironment and an image processing technique has been proposed, whichcauses a viewer to perceive a printed material as intended by a producerby suppressing a change in visual density of the printed material evenin a case where the illumination intensity changes (Patent Literature1).

Patent Literature 1 has disclosed an image processing technique thatoutputs image data for forming an image to be arranged in the viewingenvironment in the image output mode selected in accordance with thereflected light of the image under the viewing condition, which iscalculated based on the reflection characteristic of the image.

CITATION LIST Patent Literature

PTL 1 Japanese Patent Laid-Open No. 2016-054356

SUMMARY OF THE INVENTION

Note that, with the image processing technique disclosed in PatentLiterature 1, at least in the viewing environment in which theillumination intensity is high, the portion from the halftone portion tothe highlight portion of the printed material is overexposed, andtherefore, the printed material is perceived as if it were captured inthe state where the exposure is increased by a few stops. That is, thereis such a problem that in a case where the illumination intensifybecomes high, the appearance of a printed material changes.

The present disclosure provides a technique to generate an image inwhich a visual change depending on the viewing environment issuppressed.

The present disclosure is an image processing apparatus including: animage processing apparatus that generates, in accordance with intensityof light with which an image printed based on input image data isirradiated, print image data on the image from the input image data, andincludes: an acquisition unit configured to acquire a viewing conditionunder which the image is viewed; a prediction unit configured to predicta print luminance characteristic corresponding to print image data onthe image based on the viewing condition and a reflection characteristiccorresponding to print image data on the image; a derivation unitconfigured to derive a target luminance characteristic under the viewingcondition based on the print luminance characteristic; a setting unitconfigured to set a tone conversion characteristic that converts theinput image data into print image data on the image based on the printluminance characteristic and the target luminance characteristic; and ageneration unit configured to generate output image data on the image byconverting the input image data by using the tone conversioncharacteristic, and the derivation unit drives, in a case where areproduction range of an illumination intensity in the print luminancecharacteristic is different, the target luminance characteristic so thata linear area of an output luminance in a case where the reproductionrange is relatively large is larger than a linear area of an outputluminance in a case where the reproduction range is relatively small.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a print luminance that changes depending onan illumination intensity in a conventional gamma curve;

FIG. 2 is a block diagram of an image processing apparatus;

FIG. 3 is a function block diagram of the image processing apparatus;

FIG. 4 is a diagram showing a spectrophotometer used in measurement of adiffuse reflection characteristic;

FIG. 5 is a diagram showing a printed material reflection characteristicstored in a reflection characteristic storage unit;

FIG. 6 is a function block diagram of a print processing unit;

FIG. 7 is a diagram showing a GUI provided by a viewing conditionacquisition unit;

FIG. 8 is a flowchart showing a procedure of image processing in animage processing apparatus;

FIG. 9 is a diagram showing a target luminance characteristic and aconversion characteristic;

FIG. 10 is a diagram showing a setting method of the target luminancecharacteristic in a target luminance characteristic setting unit;

FIG. 11 is a diagram showing the target luminance characteristiccorresponding to a print luminance maximum value;

FIG. 12 is a diagram explaining reflected light received by the eye of aviewer from a printed material arranged in a general viewingenvironment;

FIG. 13 is a function block diagram of an image processing apparatus;

FIG. 14A is a diagram showing a variable angle measuring unit used inmeasurement of a specular reflection characteristic;

FIG. 14B is a diagram showing the variable angle measuring unit used inmeasurement of the specular reflection characteristic;

FIG. 15 is a diagram showing a printed material reflectioncharacteristic stored in the reflection characteristic storage unit;

FIG. 16 is a diagram showing the printed material reflectioncharacteristic stored in the reflection characteristic storage unit;

FIG. 17 is a diagram showing a GUI provided by the viewing conditionacquisition unit;

FIG. 18 is a diagram showing a change in density that is perceivedresulting from an exhibition environment;

FIG. 19 is a diagram showing luminance of a brightest portion of animage, luminance of a background of a non-image portion, and luminanceof a darkest portion of an image in an exhibition environment;

FIG. 20 is a diagram showing a GUI provided by the viewing conditionacquisition unit;

FIG. 21 is a diagram showing a tentative target luminancecharacteristic; and

FIG. 22 is a diagram showing a setting method of the tentative targetluminance characteristic in the target luminance characteristic settingunit.

DESCRIPTION OF THE EMBODIMENTS

In the following, preferred embodiments of the present invention areexplained in detail with reference to attached drawings. The followingembodiments are not intended to limit the present invention and allcombinations of features explained in the present embodiments are notnecessarily indispensable to the solution of the present invention.

(Brightness of Printed Material Perceived Depending on IlluminationIntensity)

First, before explanation of the embodiments of the present invention,factors by which the brightness of a printed material is perceiveddifferently depending on the illumination intensity in the viewingenvironment are explained by using FIG. 1. FIG. 1 is a diagram showing arelationship between a scene luminance [cd/m²] and a print luminance[cd/m²] in a case where the illumination intensity is set to (a) normal(300 to 1,000 [lx]) and in a case where it is set to (b) high (1,000[lx] or more) by using an input/output characteristic gamma curveregarded as being favorable conventionally. In FIG. 1, a black circle“•” shown in the drawing indicates a skin area.

In the left field in the table in FIG. 1, an input/output characteristicgamma curve (S-shaped) 1001 regarded as being favorable conventionallyindicates that the output pixel value is larger than the input pixelvalue. Specifically, in the portion from the halftone portion to thehighlight portion, that is, in an area (1002) in which the curve isconvex upward, the output pixel value is greater than the input pixelvalue. That is, the printed material becomes brighter.

Then, a relationship between the scene luminance [cd/m²] and the printluminance [cd/m²] in a case where the illumination intensity is set to(a) normal (300 to 1,000 [lx]) by using the input/output characteristicgamma curve (S-shaped) 1001 regarded as being favorable conventionallyis shown in the center field in the table in FIG. 1.

By referring to the center field in the table in FIG. 1, it is knownthat the relationship between the scene luminance and the printluminance keeps linearity and the luminance values are about the same inthe luminance range less than or equal to an important area (1005), suchas the skin area. The reason for this is that the MAX value of the printluminance viewed in the normal illumination (300 to 1,000 [lx])environment is 100 to 300 [cd/m²] and this is generally narrow comparedto the MAX value of the actual scene luminance (1,000 [cd/m²] or more).

That is, although for the input/output characteristic gamma curve(S-shaped) 1001 regarded as being favorable conventionally, the outputpixel value is set great compared to the input pixel value, the MAXvalue of the print luminance is as small as 100 to 300 [cd/m²]. Becauseof this, in the luminance range less than or equal to the important area(1005), such as the skin area, the slope of the scene luminance and thatof the print luminance are substantially the same as a result.

An area 1003 in which the input/output characteristic gamma curve(S-shaped) 1001 regarded as being favorable conventionally is convexdownward is the characteristic for correcting black floating of print tobe linear. Because of this, in many cases, the print luminance in theshadow portion is kept linear with respect to the scene luminance as aresult.

Further, a relationship between the scene luminance [cd/m²] and theprint luminance [cd/m²] in a case where the illumination intensity isset to (b) high (1,000 [lx] or more) by using the input/outputcharacteristic gamma curve (S-shaped) 1001 regarded as being favorableconventionally is shown in the right field in the table in FIG. 1.

By referring to the right field in the table in FIG. 1, it is known thatthe luminance values are not the same although the relationship betweenthe scene luminance and the print luminance keeps linearity in theluminance range less than or equal to an important area (1007), such asthe skin area. The reason for this is that the input/outputcharacteristic gamma curve (S-shaped) 1001 regarded as being favorableconventionally is nonlinear and the output pixel value is set greaterthan the input pixel value. That is, despite that the MAX value of theprint luminance and the MAX value of the scene luminance aresubstantially the same luminance values (about 1,000 [cd/m²]), theluminance value of the print luminance is obviously set greater by theinput/output characteristic gamma curve (S-shaped) regarded as beingfavorable conventionally. Because of this, the printed material isviewed as if it were captured with the exposure being increased by a fewstops. That is, the brightness of the printed material is vieweddifferently (the appearance is perceived differently) depending on theillumination intensity.

Then, in order to avoid that the brightness of a printed material isviewed (perceived) differently, it is necessary to predict in advancehow the print luminance characteristic changes in accordance with theillumination intensity. It is possible to predict the print luminancecharacteristic at least from the print diffuse reflection characteristicand the illumination intensity. In addition, it is possible to predictthe print luminance characteristic with a higher accuracy by using theprint specular reflection characteristic and the light sourcedistribution.

In the following, in a first embodiment, the print luminance perceivedby a viewer is predicted by setting the illumination intensity in anilluminating apparatus as the illumination intensity and using the printdiffuse reflection characteristic measured in advance. In addition,image processing for generating image data for print output inaccordance with the viewing environment is explained.

First Embodiment (Configuration of Apparatus)

FIG. 2 is a block diagram showing an image processing apparatusaccording to the present embodiment. As shown in FIG. 2, an imageprocessing apparatus 100 comprises an input unit 101, a display unit102, a storage unit 103, a CPU 104, a ROM 105, a RAM 106, acommunication unit 107, an output unit 108, and an image outputapparatus 111. Further, those units are connected so as to be capable ofcommunication by a system bus 109.

The image processing apparatus 100 is implemented by supplying programsfor implementing image processing, to be described later, to a computerdevice, such as a personal computer, a tablet, and a smartphone.

The input unit 101 is a serial bus interface, such as USB (UniversalSerial Bus). To the input unit 101, an input device, such as a keyboardand a mouse, and an image input device, such as a memory card reader, adigital camera, and a scanner, are connected.

The display unit 102 is a monitor or the like and displays userinstructions and image data, which are input via the input unit 101 bythe CPU 104, a graphical user interface (GUI), a processing progress ofimage processing, processing results, and the like. As described above,in a case where a table or a smartphone is made use of as the imageprocessing apparatus 100, the input unit 101 and the display unit 102are laminated and configured as a touch panel.

The storage unit 103 is a storage medium, such as a hard disk drive(HDD) and a solid state drive (SSD), in which various programs and avariety of kinds of data are stored. The programs stored in the storageunit 103 include programs for implementing image processing, to bedescribed later.

The CPU (Central Processing Unit) 104 executes an OS (Operating System)and various programs stored in the storage unit 103 or the ROM 105 byusing the RAM 106 as a work memory. Further, the CPU 104 communicateswith a server apparatus or another computer device on a network 110 viathe communication unit 107.

Specifically, the CPU 104 receives a variety of programs and data fromthe server apparatus, another computer device, and the like on thenetwork 110, and performs processing, provides data on the processingresults to the server apparatus or another computer device on thenetwork 110, and so on. The computer device with which the CPU 104 cancommunicate includes the image output apparatus 111 and it is possiblefor the CPU 104 to output image data to the image output apparatus 111via the communication unit 107. In addition, the CPU 104 controlsconfigurations, to be described later, via the system bus 109.

The ROM (Read Only Memory) 105 stores the OS and various programs asdescribed above. The RAM (Random Access Memory) 106 is used as a workmemory for the CPU 104 to operate and further, used as an image memoryfor temporarily storing image data.

The communication unit 107 is a network interface for connecting to awired or a wireless network, such as Ethernet (registered trademark),Bluetooth (registered trademark), Wi-Fi (registered trademark), and P2P.

The output unit 108 is a serial bus interface, such as USB, and outputsimage data and the like to the image output apparatus 111 and a memorycard writer, which are connected to the serial bus.

Although FIG. 2 shows an example in which the image processing apparatus100 and the image output apparatus 111 are configured as separateapparatuses, it is possible to apply the present invention to an imageforming apparatus that integrally configures the image processingapparatus 100 and the image output apparatus 111 into one apparatus. Inaddition, it is also possible to apply the present invention to an imagecopying apparatus comprising an image reading apparatus.

(Function Configuration of Image Processing Apparatus)

Next, by using FIG. 3, the function configuration of the imageprocessing apparatus 100 is explained. FIG. 3 is a function blockdiagram of the image processing apparatus 100. The functions shown inFIG. 3 are implemented by supplying programs for implementing thesefunctions to the image processing apparatus 100 shown in FIG. 2 andfurther the image processing apparatus 100 executing the programs.

Upon receipt of the input of image data by instructions from a user, animage data input unit 201 stores the input image data in a predeterminedbuffer allocated to the RAM 106 and the like. A luminance conversioncharacteristic input unit 202 receives (acquires) a characteristic forconverting the pixel values of the image data input by the image datainput unit 201 into pixel values whose luminance is linear.

As the luminance conversion characteristic, it may also be possible touse a lookup table for converting input image data into image data(pixel values) whose luminance is linear. Further, in a case where theinput image data has a publicly known y value for the luminance, it issufficient to store a value obtained by performing inverse y conversionfor the y value. For example, it is assumed that the image data input tothe image data input unit 201 is an sRGB image. In that case, it ispublicly known that y=0.45 is applied to the luminance of the sRGBimage, and therefore, it is sufficient to input y=2.2, which is theinverse of y=0.45, to the luminance conversion characteristic input unit202 and cause the image processing apparatus 100 to store it. In eithercase, the image that is input to the image data input unit 201 is onlyrequired to be input image data whose correspondence relationship withthe luminance value of an object is already known.

A luminance calculation unit 203 converts the image data input to theimage data input unit 201 into image data (pixel values) whose luminanceis linear by using the luminance conversion characteristic input to theluminance conversion characteristic input unit 202. Here, the image datathat is input to the image data input unit 201 is only required to beimage data whose correspondence relationship with the luminance value ofan object is already known. Then, it is only required for the luminancecalculation unit 203 to be capable of converting the input image datainto the image data that can be regarded as being substantially linearwith respect to the luminance value based on the correspondencerelationship. In a case where it is possible to regard the image datainput to the image data input unit 201 as being substantially linearwith respect to the luminance value, the luminance conversioncharacteristic input unit 202 and the luminance calculation unit 203 areno loner the indispensable configurations (functions).

A viewing condition acquisition unit 204 acquires the viewing conditionset by a user by using the GUI shown in FIG. 7, to be described later. Adiffuse reflection characteristic acquisition unit 205 acquires thediffuse reflection characteristic of the image output by the imageoutput apparatus 111 by, for example, a colorimeter or a variable anglemeasuring unit. A reflection characteristic storage unit 206 stores thediffuse reflection characteristic (printed material reflectioncharacteristic) acquired by the diffuse reflection characteristicacquisition unit 205.

Here, by using FIG. 4, measurement of the diffuse reflectioncharacteristic by a general spectral colorimeter is explained. In themeasurement by a spectral colorimeter, as shown in FIG. 4, illuminationlight 302 is arranged in a direction of an incidence angle of 45 degreeswith respect to a printed material 301. Then, the light irradiated fromthe illumination light 302 and reflected from the printed material 301is received by a light receiving unit 303 arranged in a direction of areflection angle of 0 degrees. By performing measurement as describedabove, in the light receiving unit 303 of the spectral colorimeter,specular reflected light 305 in accordance with the specular reflectioncharacteristic of the printed material 301 is not measured and onlydiffuse-reflected light 304 from the printed material 301 is received(measured).

In the present embodiment, the diffuse reflection characteristic isacquired by printing an input RGB image (eight bits) whose luminance islinear on the printer side without performing tone conversion andmeasuring the light reflected from the printed (output) patches by thespectral colorimeter. The acquisition of the diffuse reflectioncharacteristic is performed by printing an input image (white ((R, G,B)=(255, 255, 255)) to black ((R, G, B)=(0, 0, 0)) without performingtone conversion in a tone conversion unit 210 and using the printedpatch. The acquired diffuse reflection characteristic is stored in thereflection characteristic storage unit 206 as the printed materialreflection characteristic. Further, the reflection characteristicstorage unit 206 is allocated to, for example, the storage unit 103 orthe like.

In the present embodiment, the printed material reflectioncharacteristic is acquired from each portion obtained by equallydividing the portion from the brightest portion (that is, the whitepatch formed from the image data whose luminance is the maximum) to thedarkest portion (that is, the black patch formed from the image datawhose luminance is the minimum) of the input image data into fiveportions. Specifically, the input RGB image whose luminance is linear isequally divided into five images on a gray line and the printed materialreflection characteristic relating to each piece of image data isacquired without performing tone conversion in the tone conversion unit210. That is, for the five patches of the input images whose luminanceis linear (R, G, B)=(255, 255, 255), (192, 192, 192), (128, 128, 128),(64, 64, 64), and (0, 0, 0), the printed material reflectioncharacteristic relating to each piece of image data is acquired.

The number of images (patches) from each of which the printed materialreflection characteristic is acquired is not necessarily limited tothis. Consequently, for example, it is also possible to acquire theprinted material reflection characteristic for all the RGB values(256×256×256 sixteen millions), or for the RGB values (9×9×9=729)obtained by equally thinning the RGB values of 0 to 255 into nine RGBvalues.

Next, by using FIG. 5, the printed material reflection characteristicstored in the reflection characteristic storage unit 206 is explained.FIG. 5 is a diagram showing the printed material reflectioncharacteristic that is stored in the reflection characteristic storageunit 206 and in more detail, showing an example in which the CIEXYZvalues of the diffuse reflection characteristic corresponding to theinput image whose luminance is linear are stored as a table.

It is also possible to use the CIELAB values or only the luminance valueY in place of the CIEXYZ values.

Returning to FIG. 3, a print luminance value prediction unit 207calculates (predicts) the luminance of the diffuse-reflected light ofthe printed material in the viewing environment from the illuminationintensity acquired from the viewing condition acquisition unit 204 andthe printed material reflection characteristic stored in the reflectioncharacteristic storage unit 206. A target luminance characteristicsetting unit 208 sets a target luminance characteristic to be reproducedas a printed material based on the print luminance predicted by theprint luminance value prediction unit 207. As will be described later,in a case where saturation is used in place of luminance, the targetluminance characteristic setting unit 208 sets a target saturationcharacteristic to be reproduced as a printed material as a targetsaturation characteristic setting unit.

A conversion characteristic setting unit 209 sets a tone conversioncharacteristic for conversion into image data to be output to the printprocessing unit 211 based on the difference between the target luminancecharacteristic set by the target luminance characteristic setting unit208 and the print luminance predicted by the print luminance valueprediction unit 207.

The tone conversion unit 210 performs tone conversion for the inputimage data whose luminance is linear, which is output from the luminancecalculation unit 203, by using the tone conversion characteristic set bythe conversion characteristic setting unit 209.

A print processing unit 211 outputs print image data after performingprocessing for print (for printing) for the image data (output imagedata) converted by the tone conversion unit 210. In the presentembodiment, it is assumed that the pixel value of the above-describedprint image data and the luminance of the printed material are in aliner (proportional) relationship. Further, the print image data issupplied to the image output apparatus 111 via the output unit 108 andimage forming processing is performed.

(Print Processing Unit)

Next, by using FIG. 6, the function configuration of the printprocessing unit 211 is explained. FIG. 6 is a function block diagram ofthe print processing unit 211. The print processing unit 211 comprises,as its functions, a CMS processing unit 401, a color separationprocessing unit 402, a halftone processing unit 403, a color profile404, a color separation table 405, and a halftone parameter 406.

The CMS (Color Management System) processing unit 401 performs colormatching processing for image data stored in the buffer by referring tothe color profile 404 designed in advance.

The color separation processing unit 402 performs color separation forthe image data for which the color matching processing has beenperformed into printing materials mounted on the image output apparatus111 by referring to the color separation table 405 designed in advance.For example, in a case where printing materials of six colors ofCMYKLcLm are mounted on the image output apparatus 111, the colorseparation is performed for the RGB image data into printing materialdata indicating the amount of each printing material of CMYKLcLm.

The halftone processing unit 403 binarizes each piece of printingmaterial data for which the color separation has been performed bybinarization processing, such as the error diffusion method and thedither method, by referring to an error diffusion coefficient, such asthe halftone parameters 406, and a threshold value matrix. In a casewhere the image output apparatus 111 is an ink jet printer, the imageoutput apparatus 111 forms, upon receipt of halftone image data, animage on a printing medium by controlling ejection of corresponding inkin accordance with each piece of printing material data.

(Viewing Condition Acquisition Unit)

Next, by using FIG. 7, the GUI provided by the viewing conditionacquisition unit 204 is explained. A user sets the viewing condition byusing the GUI shown in FIG. 7. A user selects “Candidate selection” inwhich the illumination intensity on a printed material is inputintuitively and “Numerical value setting” in which the illuminationintensity is input with a numerical value (physical value) by checking acheckbox on the GUI shown in FIG. 7.

In a case where “Candidate selection” is selected, the illuminationintensity is selected from candidates, for example, such as very bright(daytime outdoor), bright (illumination in art museum), moderate(office), and slightly dark (slightly dark office (ordinary home)). Tothe candidate that is selected as “Candidate selection”, an illuminancelux corresponding to the candidate is set and for example, in a casewhere moderate (office) is selected, the subsequent processing isperformed on the assumption that 800 [lx] is selected. Further, in acase where “Numerical value setting” is selected, a specificillumination intensity is selected by an illumination intensity (valueof illuminance lux [lx]) on the printed material being input in a textbox or by moving a slider bar to the left or right. By the above, theillumination intensity with which the surface of the printed material isirradiated is acquired and set by the viewing condition acquisition unit204.

In the above-described embodiment, although explanation is given byusing the illuminance [lx] as the illumination intensity (luminance),the illumination intensity is not necessarily limited to this and forexample, it is also possible to use luminance [cd/m²] and [nit]. Inaddition, in order to cause the illumination intensity to be input moreaccurately, it may also be possible to display a note to the effect thatthe illuminance measurement by an illuminometer is necessary on theprinted material that is posted on the GUI.

(Image Processing)

Next, by using FIG. 8, the image processing in the image processingapparatus 100 is explained. FIG. 8 is a flowchart showing the procedureof the image processing in the image processing apparatus 100. Eachsymbol S in the following means that the step is a step in theflowchart. The luminance calculation unit 203 converts the image datainput to the image data input unit 201 into input image data whoseluminance is linear by using the luminance conversion characteristicinput to the luminance conversion characteristic input unit 202 (S501).

The viewing condition acquisition unit 204 acquires a viewing condition(illumination intensity Lt [lx]) selected by a user (S502)

In a case where the viewing condition is acquired by the viewingcondition acquisition unit 204 (S502), the print luminance valueprediction unit 207 acquires a diffuse reflection characteristic (Pd)from the reflection characteristic storage unit 206 (S503). The printluminance value prediction unit 207 calculates a luminance Cd of thediffuse-reflected light of the printed material based on the viewingcondition (illumination intensity Lt [lx]) and the diffuse reflectioncharacteristic (Pd), which are acquired (S504).

The luminance Cd of the diffuse-reflected light of the printed materialis calculated by the following formula.

Cd=PdY/100×Lt/π[cd/m ²]  (1)

Here, π indicates the ratio of the circumference of a circle to itsdiameter and PdY indicates the Y component in the tri-stimulus valuesXYZ of the diffuse reflection characteristic.

The print luminance value prediction unit 207 determines whether or notthe luminance Cd of the diffuse-reflected light has been calculated forall the patches (S505). Then, in a case where it is determined that thecalculation of the luminance Cd of the diffuse-reflected light has notbeen completed for all the patches (No at S505), the image processingapparatus 100 returns the processing to S504 and calculates theluminance Cd of the diffuse-reflected light for all the patches.

As described above, in the present embodiment, for the input RGB image(whose luminance is linear) obtained by equally dividing the gray lineinto five portions, the diffuse reflection characteristic relating toeach piece of image data is acquired. That is, for the input image whoseluminance is linear (R, G, B)=(255, 255, 255), (192, 192, 192), (128,128, 128), (64, 64, 64), and (0, 0, 0), the printed material reflectioncharacteristic relating to each piece of image data is acquired.

In a case where the luminance Cd of the diffuse-reflected light of theprinted material is calculated by the print luminance value predictionunit 207, the target luminance characteristic setting unit 208 sets(derives) a target luminance characteristic to be reproduced as theprinted material based on the calculated luminance Cd of thediffuse-reflected light of the printed material (S506).

The target luminance characteristic is set so that in a case where thereproduction range of the print luminance characteristic is different,the slope in the linear area of the output luminance on a condition thatthe reproduction range is relatively small and the slope in the lineararea of the output luminance on a condition that the reproduction rangeis relatively large become the same.

In the following, in a case where the reproduction range of the printluminance characteristic is considered as the difference between themaximum value of the print luminance and the minimum value of the printluminance, as the illumination intensity [lx] becomes high, generally,the reproduction range of the print luminance characteristic becomeslarge.

Here, for example, as shown in FIG. 5, it is supposed that the printedmaterial having the range in which the diffuse reflection characteristicPdY of print is 0.77 to 90.3 is irradiated with an illumination whoseillumination intensities [lx] are, for example, 300 and 3,000, which areten times different, as the illumination intensity [lx]. Then, thereproduction range of the print luminance characteristic is calculatedby formula (1).

In a case where the illumination intensity is 300 [lx], the printluminance characteristic Cd is 0.7 to 86.3 [cd/m²] and (the maximumvalue of the print luminance—the minimum value of the print luminance)is 85.6. On the other hand, in a case where the illumination intensityis 3,000 [lx], the print luminance characteristic Cd is 7.4 to 862[cd/m²] and (the maximum value of the print luminance—the minimum valueof the print luminance) is 855. That is, the higher the illuminanceintensity [lx] becomes, the larger the reproduction range of the printluminance characteristic becomes.

It is also possible to approximately calculate the reproduction range ofthe print luminance characteristic from the maximum value of the printluminance. The reason the calculation is possible in this manner is thatthe minimum value of the print luminance is sufficiently smaller thanthe maximum value of the print luminance and even in a case where thereproduction range of the print luminance characteristic is calculatedby using the maximum value of the print luminance, the same value isobtained in many cases.

In addition, in view of the above-described contents, in a case wherethe reproduction range of the print luminance characteristic isdifferent, the setting is performed so that the slope in the linear areaof the output luminance in a case where the reproduction range isrelatively small and the slope in the linear area of the outputluminance in a case where the reproduction range is relatively largebecome the same.

Next, by using FIG. 9, the setting of the target luminancecharacteristic is explained. FIG. 9 shows s print luminance predictedvalue Cd of a patch, which is predicted in accordance with theillumination intensity, and a target luminance characteristic T_Cd thatis set based on the print luminance predicted value.

In FIG. 9, the print luminance predicted value Cd is calculated based onformula (1) from a Y-value (PdY) of the diffuse reflectioncharacteristic and the illumination intensity Lt [lx]. Based on formula(1), in FIG. 9, in a case where the illumination intensity is normal(300 [lx]), a maximum value Cd_Max (2001) of the print luminancepredicted value Cd of a patch is about 100 [cd/m²]. On the other hand,in a case where the illumination intensity is high (3,000 [lx]), themaximum value Cd_Max (2002) of the print luminance predicted value Cd ofa patch is about 1,000 [cd/m²].

The illuminating apparatus device that is used in a case where theillumination intensity is normal (300 [lx]) as described above is ahandy-type, simple illumination. On the other hand, the illuminatingapparatus that is used in a case where the illumination intensity ishigh (3,000 [lx]) is a comparatively large illumination.

The target luminance characteristic T_Cd in a case where theillumination intensity is normal (300 [lx]) has a linear characteristicin the portion from the shadow portion to the halftone portion (area inwhich the input pixel value is smaller than 64 (2005)). In the portionfrom the halftone portion to the highlight portion (area in which theinput pixel value is greater than 64 (2005)), the conversioncharacteristic bends and the target luminance characteristic T_Cd has anonlinear characteristic (2003). On the other hand, the target luminancecharacteristic T_Cd in a case where the illumination intensity is high(3,000 [lx]) has a linear characteristic in the portion from the shadowportion to the highlight portion (2004).

As described above, in a case where the reproduction range of the printluminance characteristic is different, the setting is performed so thatthe slope in the linear area of the output luminance in a case where thereproduction range is relatively small and the slope in the linear areaof the output luminance in a case where the reproduction range isrelatively large become the same.

In addition, in the example described above, although the example isshown in which in a case where the illumination intensity is high (3,000[lx]), the target luminance characteristic has a linear characteristicin the portion from the shadow portion to the highlight portion, thetarget luminance characteristic is not necessarily limited to this.Consequently, it may also be possible to cause the target luminancecharacteristic to have a linear characteristic in the portion from theshadow portion to the highlight portion in a case where the illuminationintensity is lower than the 3,000 [lx] (for example, 1,000 [lx]).Further, on the contrary, it may also be possible to cause the targetluminance characteristic to have a nonlinear characteristic in thehighlight portion (that is, area in which the input pixel value isgreater than 128) in a case where the illumination intensity is higherthan 3,000 [lx] (for example, 5,000 [lx]). In either case, it is onlyrequired for the setting to be performed so that in a case where thereproduction range of the print luminance characteristic is different,the slope in the linear area of the target luminance characteristic in acase where the reproduction range is relatively small and the slope inthe linear area of the target luminance characteristic in a case wherethe reproduction range is relatively large become the same.

As a supplement, it is possible to determine the distinction between thelinear area and the nonlinear area by a change in the feature amount,such as the difference between the pixel value and the previous (ornext) pixel value (differential). For example, a difference of thetarget luminance characteristic between the pixel value and the previous(or next) pixel value is sequentially calculated in order from theshadow portion (pixel value 0). Then, in a case where the differencebetween the pixel value and the previous (or next) pixel value isconstant, the area is regarded as being linear. Further, in a case wherea difference value ΔT is greater than a predetermined amount, or lessthan a predetermined amount, the area is regarded as being nonlinear.Consequently, for example, in distinguishing between the linear area andthe nonlinear area, in a case where the change ΔT in the differencevalue is equal to or greater than 3, or the change ΔT in the differencevalue is equal to or less than ⅓, it is determined that the area is thenonlinear area.

Next, by using FIG. 10, the setting method of the target luminancecharacteristic T_Cd in the target luminance characteristic setting unit208 is explained. The target luminance characteristic T_Cd that is setby the target luminance characteristic setting unit 208 is calculatedfrom two different tables (Tbl_1, Tbl_2) prepared in advance and afunction of a weighting a value in accordance with the maximum valueCd_Max [cd/m²] of the print luminance predicted value Cd.

The two different tables are Tbl_1 (3001) having nonlinearity (ΔT isequal to or greater than 3 or equal to or less than ⅓) and Tbl_2 (3002)having linearity in the portion from the shadow portion to the highlightportion and the tables are set to that the slopes in the linear areas ofthe output luminance become the same. Further, as the function, afunction in which the weighting a value in accordance with the maximumvalue Cd_Max [cd/m²] of the print luminance predicted value Cd is in alinear relationship with Cd_Max (3003) is used. That is, the functionsare set so that as the maximum value Cd_Max of the print luminancepredicted value Cd becomes greater, the weighting a value also becomesgreater.

Based on the premise described above, the target luminancecharacteristic T_Cd in the target luminance characteristic setting unit208 is calculated by the following formula.

T_Cd(In)=(1−α(Cd_Max))×Tbl_1(In)+α(Cd_Max)×Tbl_2(In)  (2)

In is the input pixel vale (0≤In≤255). Further, Tbl_1 (In) is theluminance value of Tbl_1 in the input pixel value In and Tbl_2 (In) isthe luminance value of Tbl_2 in the input pixel value In. Then, thetarget luminance characteristic T_Cd calculated by the above formula ina case where the weighting a value is varied as α=0.00 (3004), α=0.33(3005), α=0.66 (3006), and α=1.00 (3007) is shown on the lower side inFIG. 10.

As shown in FIG. 10, even in a case where the a value is varied (even ina case where the reproduction range of the print luminance is varied),in the area in which the input pixel value In and the target luminancecharacteristic T_Cd have a linear relationship, it is known that theslopes are the same. That is, in a case where the reproduction range ofthe print luminance characteristic is different, the setting isperformed so that the slope in the linear area of the output luminancein a case where the reproduction range is relatively small and the slopein the linear area of the output luminance in a case where thereproduction range is relatively large become the same.

In FIG. 10, the example is shown in which the target luminancecharacteristic T_Cd is set so that the slopes in the linear areas of theoutput luminance become the same even in a case where the reproductionrange of the print luminance characteristic is different by using thetwo different tables. Note that the setting of the target luminancecharacteristic T_Cd is not necessarily limited to the method describedabove and for example, it may also be possible to define the targetluminance characteristic T_Cd by a spline function and set the curve ofthe spline function so that the slopes in the linear areas of the outputluminance become the same.

Here, returning to FIG. 8, the conversion characteristic setting unit209 sets a conversion characteristic Out_Tbl by using the printluminance predicted value Cd of a patch, which is predicted by the printluminance value prediction unit 207, and the target luminancecharacteristic T_Cd set by the target luminance characteristic settingunit 208 (S507). The conversion characteristic Out_Tbl is set so thatthe print luminance predicted value Cd becomes the target luminancecharacteristic T_Cd.

Here, FIG. 9 is referred to again and the print luminance predictedvalue Cd and the target luminance characteristic T_Cd are compared. InFIG. 9, a graph that compares tendencies of the print luminancepredicted value Cd and the target luminance characteristic T_Cd in acase where the illumination intensity is normal (300 [lx]) is indicatedby 2006. Further, a graph that compares tendencies of the printluminance predicted value Cd and the target luminance characteristicT_Cd in a case where the illumination intensity is high (3,000 [lx]) isindicated by 2007.

As indicated by symbol 2006 and symbol 2007 in FIG. 9, in a case wherethe illumination intensity is normal (300 [lx]), it is known that thetarget luminance characteristic T_Cd becomes larger than the printluminance predicted value Cd. On the other hand, in a case where theillumination intensity is high (3,000 [lx]), it is known that the printluminance predicted value Cd and the target luminance characteristicT_Cd substantially overlap. That is, in a case where the illuminationintensity is high (3,000 [lx]), the target luminance characteristic T_Cdand the print luminance predicted value Cd are substantially the same.

Here, as expressed in the above formula (1), the print luminancepredicted value Cd is in a proportional relationship with theillumination intensity Lt [lx] (that is, in a case where theillumination intensity Lt is halved, the print luminance predicted valueCd is also halved and in a case where the illumination intensity Lt [lx]is doubled, the print luminance predicted value Cd is also doubled).

Consequently, in a case where the conversion characteristic Out_Tbl isset based on the ratio of the print luminance predicted value Cd to thetarget luminance characteristic T_Cd for each tone in the graphs 2006and 2007, it is possible to put the print luminance value close to thetarget luminance characteristic in all the tones.

Because of this, the conversion characteristic Out_Tbl is set by thefollowing formula. In is the input pixel value (0≤In≤255), T_Cd (In) isthe target luminance characteristic in the input pixel value In, and Cd(In) is the print luminance predicted value in the input pixel value In.

Out_Tbl(In)=(T_Cd(In)/Cd(In))×255  (3)

The conversion characteristic Out_Tbl in a case where the illuminationintensity is normal (300 [lx]) is indicated by 2008 in FIG. 9 and theconversion characteristic Out_Tbl in a case where the illuminationintensity is high (3,000 [lx]) is indicated by 2009 in FIG. 9. As shownin FIG. 9, in a case where the illumination intensity is normal (300[lx]) and in a case where the illumination intensity is high (3,000[lx]), the setting is performed so that the slopes in the linear areasof the output luminance become the same.

That is, in a case where the reproduction range of the predicted printluminance characteristic is different, the setting is performed so thatthe slope in the linear area of the output luminance in a case where thereproduction range is relatively small and the slope in the linear areaof the output luminance in a case where the reproduction range isrelatively large become the same.

Here, returning to FIG. 8, the tone conversion unit 210 performs toneconversion for the image data calculated by the luminance calculationunit 203 by using the conversion characteristic Out_Tbl set by theconversion characteristic setting unit 209 and outputs the data to theprint processing unit 211 (S508). Due to this, the image processingshown in FIG. 8 is terminated (S508).

As explained above, in the present embodiment, the print luminanceperceived by a viewer is predicted by using the viewing condition andthe print diffuse reflection characteristic measured in advance. Inaddition, it is described that in a case where the reproduction range ofthe predicted print luminance characteristic is different, the imagedata for the print control of the image output apparatus is changed sothat the slopes in the linear areas of the output luminance become thesame. That is, it is described that an image in which a visual changedepending on the viewing environment is suppressed is generated.

Further, in the embodiment described above, based on the predicted printluminance characteristic, the luminance conversion characteristic is setso that the slopes in the linear areas of the output luminance becomethe same. Note that it may also be possible to predict the printsaturation from tri-stimulus values PdX, PdY, and PdZ of the diffusereflection characteristic shown in FIG. 5. Then, in a case where thereproduction range of the predicted print saturation characteristic isdifferent, it may also be possible to set the conversion characteristicso that the slopes in the linear areas of the output saturation becomethe same.

Second Embodiment

In the first embodiment described above, in a case where thereproduction range of the predicted print luminance characteristic isdifferent, the luminance conversion characteristic is set so that theslopes in the linear areas of the output luminance become the same.Further, the conversion characteristic is set so that the printluminance predicted value Cd becomes the target luminance characteristicT_Cd (FIG. 10) calculated based on the synthesis (formula (2)) of thetwo different tables.

Note that, in the target luminance characteristic set by the methoddescribed above, the area in which the output luminance characteristicbecomes the curve from the straight line (area in which nonlinearitybegins) is the same even in a case where the reproduction range of theprint luminance characteristic is different. Specifically, for example,the output luminance characteristic of Tbl_1 (3001) shown in FIG. 10becomes the curve from the straight line in the vicinity of 10 of theinput image value In and in the vicinity (3008) of 20 [cd/m²] of theoutput luminance Tbl_1. Further, the area in which the output luminancecharacteristic becomes the curve from the straight line is also the sameeven in a case where the reproduction range of the print luminancecharacteristic is different (3008 to 3011). That is, the linear area ofthe output luminance characteristic is the same.

Note that, in a case where the reproduction range of the print luminancecharacteristic is different, the linear area of the output luminancecharacteristic does not need to be the same. Rather, it must be possibleto represent the output luminance information corresponding to the inputinformation more correctly by increasing the linear area of the outputluminance characteristic as the reproduction range of the printluminance becomes large.

Consequently, in the present embodiment, in a case where thereproduction range of the print luminance characteristic is different,on a condition that the reproduction range becomes relatively large, theconversion characteristic of the output luminance is set so that thelinear area of the output luminance becomes large. The presentembodiment is the same as the first embodiment except for the processingat S506 of the flowchart shown in FIG. 8, and therefore, here,explanation thereof is omitted.

In the first embodiment, at S506, based on the luminance Cd of thediffuse-reflected light of the printed material, which is calculated bythe print luminance value prediction unit 207, the target luminancecharacteristic to be reproduced as the printed material is set. In thepresent embodiment, the two or more target luminance characteristicsT_Cd whose sizes of the linear areas of the output luminance aredifferent are prepared and switched in accordance with the maximum valueCd_Max of the print luminance predicted value Cd. Specifically, forexample, as shown in FIG. 11, the four target luminance characteristicsT_Cd whose sizes of the linear areas of the output luminance aredifferent are prepared and the target luminance characteristics T_Cd areswitched in correspondence to the maximum value Cd_Max of the printluminance predicted value Cd.

FIG. 11 shows the target luminance characteristic T_Cd corresponding tothe print luminance maximum value and in FIG. 11, for example, in a casewhere the print luminance maximum value satisfies “Cd_Max<100”, T_Cd_1(4001) is allocated as the target luminance characteristic. Similarly,in a case where “100≤Cd_Max<200”, T_Cd_2 (4002) is allocated, in a casewhere “200<Cd_Max<500”, T_Cd_3 (4003) is allocated, and in a case where“500≤Cd_Max”, T_Cd_4 (4004) is allocated

In FIG. 11, as will be known from 4005 to 4007 in the drawing, thetarget luminance characteristic T_Cd is set so that the larger thereproduction range of the print luminance characteristic, the larger thelinear area of the output luminance becomes.

In FIG. 11, based on the predicted print luminance characteristic, theluminance conversion characteristic is set so that the linear area ofthe output luminance becomes large. Note that it may also be possible toset the saturation conversion characteristic so that the linear area ofthe output saturation becomes large based on the predicted printsaturation characteristic.

As explained above, in the present embodiment, in a case where thereproduction range of the print luminance characteristic is different,on a condition that the reproduction range becomes large relatively, theconversion characteristic of the output luminance is set so that thelinear area of the output luminance becomes large. Due to this, even ina case where the reproduction range of the print luminance is different,it is possible to represent the output luminance informationcorresponding to the input information more correctly.

Third Embodiment

In the first and second embodiments described above, the print luminance(saturation) is predicted from the illumination intensity. Then, theexample is shown in which the setting is performed so that “the slopesin the linear areas of the output luminance become the same” inaccordance with the reproduction range of the predicted print luminance(saturation). Further, the example is also shown in which the setting isperformed so that “the linear area corresponding to the luminance(saturation) of the input image increases”.

Note that there is a case where it is not possible to predict the printluminance only by the illumination intensity. In the following, the casewhere it is not possible to predict the print luminance only by theillumination intensity is illustrated by using FIG. 12. FIG. 12 is adiagram showing the way light reflected from a printed material arrangedin a general viewing environment is received by the eyes of a viewer.

In FIG. 12, a viewing position 601 corresponds to the specularreflection direction of an illumination 604 and at the viewing position601, the light (specular reflected light) included in the illuminationimage of a printed material 603 reaches the eyes of a viewer. Here, in acase where the intensity of the specular reflected light is too high, itis not possible for a viewer to recognize the color of the printedmaterial 603, and therefore, the viewer moves from the viewing position601 to a viewing position 602 at which the specular reflected light doesnot enter the eyes and views the printed material 603.

Note that, in a case where FIG. 12 is referred to, in the specularreflection direction corresponding to the positional relationshipbetween the viewing position 602 and the printed material 603, a wall606 exists. That is, in the specular reflection direction correspondingto the positional relationship between the viewing position 602 and theprinted material 603, the wall 606 exists. Because of this, the light ofthe illumination 604 is reflected from the wall 606 and reaches theprinted material 603 and further, received by the eyes of the viewer asthe specular reflected light in accordance with the specular refectioncharacteristic of the printed material 603 and recognized as the printluminance by the viewer.

Although the reflected light from the wall 606 is weak compared to thelight that reaches the printed material 603 directly from theillumination 604, the intensity thereof is not so low that the color ofthe printed material 603 cannot be recognized at the viewing position602. In addition, in a case where the light from a variety of directionsother than the specular reflection direction, for example, the lightfrom an illumination 605 also reaches the printed material 603, thelight is also received by the eyes of the viewer as thediffuse-reflected light in accordance with the diffuse reflectioncharacteristic of the printed material 603 and recognized as the printluminance.

As described above, the eyes of the viewer receive the print luminance,which is the luminance in the incidence angle direction facing thepositional relationship between the viewing angle and the printedmaterial being reflected in accordance with the specular reflectioncharacteristic, and the print luminance, which is the light from adirection other than the incidence angle direction being reflected inaccordance with the diffuse reflection characteristic of the printedmaterial 603. That is, the eyes of the viewer receive the printluminance based on the diffuse reflection and the print luminance basedon the specular reflection.

Here, in the first embodiment described above, only the print luminancebased on the diffuse reflection of the light (illumination intensity) inthe direction other than the incidence angle direction facing thepositional relationship between the viewing position and the printedmaterial (sample) is taken into consideration. That is, in the firstembodiment, the print luminance based on the specular reflection of theluminance (brightness of the ceiling and the wall) in the incidenceangle direction facing the positional relationship between the viewingposition and the printed material is not taken into consideration.

Consequently, in the present embodiment, prediction of the printluminance based on the luminance (hereinafter, luminance in theincidence angle direction) in the incidence angle direction facing thepositional relationship between the viewing position and the printedmaterial (sample) is additionally studied. Then, the tone conversioncharacteristic is set so that “the slopes in the linear areas of theoutput luminance become the same” in accordance with the reproductionrange of the predicted print luminance thereof and further, “the lineararea for the luminance of the input image increases”.

(Function Configuration of Image Processing Apparatus)

Next, by using FIG. 13, the function configuration of the imageprocessing apparatus 100 is explained. FIG. 13 is a function blockdiagram of the image processing apparatus 100. The functions shown inFIG. 13 are implemented by supplying the programs for implementing thesefunctions to the image processing apparatus 100 shown in FIG. 13 andfurther, the image processing apparatus 100 executing the programs.Other than the viewing condition acquisition unit 204, the diffusereflection characteristic acquisition unit 205, the reflectioncharacteristic storage unit 206, the print luminance value predictionunit 207, and the print processing unit 211, the functions are the sameas those of the image processing apparatus 100 of the first embodiment,and therefore, explanation is omitted here.

The viewing condition acquisition unit 204 acquires the viewingcondition set by a user by using a GUI shown in FIG. 17, to be describedlater. The diffuse reflection characteristic acquisition unit 205acquires the diffuse reflection characteristic of an image output by theimage output apparatus 111 by, for example, a colorimeter. Thereflection characteristic storage unit 206 stores, as the printedmaterial reflection characteristic, the diffuse reflectioncharacteristic acquired by the diffuse reflection characteristicacquisition unit 205 and the specular reflection characteristic acquiredby a specular reflection characteristic acquisition unit 212. The printluminance value prediction unit 207 calculates (predicts) thediffuse-reflected light of the printed material in the viewingenvironment and the luminance of the specular reflected light from theillumination intensity acquired by the viewing condition acquisitionunit 204, the luminance (brightness of the ceiling/wall) in theincidence angle direction, and the printed material reflectioncharacteristic stored in the reflection characteristic storage unit 206.The specular reflection characteristic acquisition unit 212 acquires thespecular reflection characteristic of the image output by the imageoutput apparatus 111 by, for example, a variable angle measuring unit.

Here, the specular reflection characteristic is measured by a generalvariable angle measuring unit shown in FIG. 14A and FIG. 14B. Here, thevariable angle measuring unit is a device for measuring a conversioncharacteristic (bidirectional reflectance distribution function: BRDF).Further, the conversion characteristic is a characteristic obtained bymeasuring the intensity of reflected light for the emitting angle(reflection angle) in a case where light is emitted from a certainangle.

The conversion characteristic is measured by irradiating a printedmaterial 701 with light from illumination light 702 arranged at aposition whose projection angle is θ and receiving the reflectionintensity of the printed material 701 by a light receiving unit 703arranged at a position whose light receiving angle is θ′ as shown inFIG. 14A. It is possible to measure the reflection intensity in all thedirections by varying the projection angle θ and the light receivingangle θ′ in the measurement of the conversion characteristic.

Further, FIG. 14B shows a measurement example of the conversioncharacteristic in a case where general glossy paper is taken as theprinted material 701. In FIG. 14B, the reflection intensity is measuredby, for example, fixing the projection angle θ at 45 degrees andchanging the light receiving angle θ′ from −90 degrees to +90 degrees.In FIG. 14B, the light emitted from the illumination light 702 isreflected from the printed material 701 and exhibits a large reflectioncharacteristic in the specular reflection direction (hereinafter,specular reflection characteristic). On the other hand, the printedmaterial 701 exhibits a small reflection characteristic in a directionother than the specular reflection direction (hereinafter, diffusereflection characteristic).

In the present embodiment, the diffuse reflection characteristic and thespecular reflection characteristic are acquired by printing the inputRGB image (eight bits) whose luminance is linear on the printer sidewithout performing tone conversion and measuring the light reflectedfrom the printed patch by a spectral colorimeter and a variable anglemeasuring unit.

The acquisition of these reflection characteristics is performed byprinting the input image (white ((R, G, B)=(255, 255, 255)) to black((R, G, B)=(0, 0, 0)) without performing tone conversion in the toneconversion unit 210 and using the printed patches. The diffusereflection characteristic and the specular reflection characteristic,which are acquired, are stored in the reflection characteristic storageunit 206 as the printed material reflection characteristic. Further, thereflection characteristic storage unit 206 is allocated to, for example,the storage unit 103 or the like.

In the present embodiment, the printed material reflectioncharacteristics (diffuse reflection characteristic and specularreflection characteristic) are acquired from each portion obtained byequally dividing the portion from the brightest portion (that is, thewhite patch formed from the image data whose luminance is the highest)to the darkest portion (that is, the black patch formed from the imagedata whose luminance is the lowest) of the input image data into fiveportions. Specifically, the input RGB image whose luminance is linear isdivided equally into five images on a gray line and the printed materialreflection characteristics relating to each piece of image data areacquired. That is, for the five patches of the input image whoseluminance is linear (R, G, B)=(255, 255, 255), (192, 192, 192), (128,128, 128), (64, 64, 64), and (0, 0, 0), the printed material reflectioncharacteristics relating to each piece of image data are acquired.

The number of images (patches) from each of which the printed materialreflection characteristics are acquired is not necessarily limited tothis. Consequently, for example, it is also possible to acquire theprinted material reflection characteristics for all the RGB values(256×256×256 sixteen millions), or for the RGB values (9×9×9=729)obtained by equally thinning the RGB values of 0 to 255 into nine RGBvalues.

Next, by using FIG. 15, the printed material reflection characteristics(diffuse reflection characteristic and specular reflectioncharacteristic) stored in the reflection characteristic storage unit 206are explained. FIG. 15 is a diagram showing the printed materialreflection characteristics that are stored in the reflectioncharacteristic storage unit 206 and in more detail, showing an examplein which the CIEXYZ values of the diffuse reflection characteristic andthe specular reflection characteristic corresponding to the input imagewhose luminance is linear are stored as a table. It is also possible touse the CIELAB values or only the luminance value Yin place of theCIEXYZ values.

In addition, it is not necessary to prepare the same number of values ofthe CIEXYZ values of the diffuse reflection characteristic (diffusereflectance) and the specular reflection characteristic (specularreflectance). Specifically, the measurement of the specular reflectioncharacteristic relatively requires time and effort compared to that ofthe diffuse reflection characteristic, and therefore, it may also bepossible to reduce the number of specular reflection characteristicscompared to that of diffuse reflection characteristics as shown in FIG.16.

(Viewing Condition Acquisition Unit)

Next, by using FIG. 17, a GUI provided by the viewing conditionacquisition unit 204 is explained. A user sets the viewing conditions byusing the GUI shown in FIG. 17. On the GUI shown in FIG. 17, a userselects “Candidate selection” in which the illumination intensity on aprinted material and the luminance in the incidence angle direction areinput intuitively and “Numerical value setting” in which theillumination intensity and the luminance in the incidence angledirection are input with a numerical value (physical value) by checkinga checkbox.

In a case where “Candidate selection” is selected, the illuminationintensity is selected from illumination intensity candidates, forexample, such as very bright (daytime outdoor), bright (illumination inart museum), moderate (office), and slightly dark (slightly dark office(ordinary home)). In addition, the luminance in the incidence angledirection is selected from luminance candidates in the incidence angledirection, for example, such as very bright (white), bright (brightgray), moderate (gray), and dark (black). To the candidate that isselected as “Candidate selection”, the illuminance lux and the luminance(brightness of ceiling/wall) in the incidence angle directioncorresponding to the candidate are set. For example, in a case wheremoderate (office) is selected as regards the illuminance lux, thesubsequent processing is performed on the assumption that 800 [lx] isselected, and in a case where moderate (gray) is selected as regards theluminance (brightness of ceiling/wall) in the incidence angle direction,the subsequent processing is performed on the assumption that 50 [cd/m²]is selected.

Further, in a case where “Numerical value setting” is selected, asregards the illumination intensity, the illumination intensity (value ofilluminance lux (Lx)) on the printed material is input in the text box,or a specific illumination intensity is selected by moving a slider barto the left or right. In addition, also as regards the luminance in theincidence angle direction, the value of the luminance [cd/m²] of theceiling or the wall, which enters from the viewing surface, is caused tobe input in the text box, or by moving the slide bar to the left andright, a specific luminance in the incidence angle direction isselected. By the above, the illumination intensity with which thesurface of the printed material is irradiated and the luminance(brightness of ceiling/wall) in the incidence angle direction areacquired and set by the viewing condition acquisition unit 204.

In the above-described embodiment, although explanation is given byusing the illuminance [lx] as the illumination intensity (luminance),the illumination luminance is not necessarily limited to this and forexample, it is also possible to use the luminance [cd/m²] and [nit]. Inaddition, in order to cause the illumination intensity to be input moreaccurately, it may also be possible to display a note to the effect thatthe illuminance measurement by an illuminometer on the printed materialthat is posted, and the measurement of the luminance in the incidenceangle direction facing the positional relationship between the viewingangle and the printed material are necessary on the GUI.

(Image Processing)

Next, by using FIG. 8, the image processing in the image processingapparatus 100 is explained. As described above, FIG. 8 is a flowchartshowing the procedure of the image processing in the image processingapparatus 100. The processing at S501 to S503 and the processing at S506to S508 are the same as those of the first embodiment, and therefore,explanation thereof is omitted here.

At S504, first, based on the viewing conditions (illumination intensityLt [lx], a luminance Wt [cd/m²] in the incidence angle direction), thediffuse reflection characteristic (Pd), and a specular reflectioncharacteristic (Rd), which are acquired, a luminance Cd_P of thediffuse-reflected light and a luminance Cd_R of the specular reflectedlight of the printed material are calculated. Further, based on theluminance Cd_P of the diffuse-reflected light and the luminance Cd_R ofthe specular reflected light of the printed material, a total luminanceCd that reaches the eyes of a viewer is calculated by the followingformula.

Cd_P=PdY/100×Lt/π[cd/m ²]  (4)

Cd_R=RdY/100×Wt[cd/m ²]  (5)

Here, π indicates the ratio of the circumference of a circle to itsdiameter, PdY indicates the Y component in the tri-stimulus values XYZof the diffuse reflection characteristic, and RdY indicates the Ycomponent in the tri-stimulus values XYZ of the specular reflectioncharacteristic.

Cd=Cd_P+Cd_R  (6)

Next, the print luminance value prediction unit 207 determines whetheror not the total luminance Cd has been calculated for all the patches(S505). Then, in a case where it is determined that the calculation ofthe total luminance Cd of the diffuse-reflected light has not beencompleted for all the patches (No at S505), the image processingapparatus 100 returns the processing to S504 and calculates the totalluminance Cd of the diffuse-reflected light for all the patches.

In the present embodiment, for the input RGB image (image whoseluminance is linear) obtained by equally dividing the gray line intofive portions, the diffuse reflection characteristic and the specularreflection characteristic relating to each piece of image data areacquired. That is, the diffuse reflection characteristic and thespecular reflection characteristic relating to each piece of image dataare acquired for the five patches of the input images whose luminance islinear (R, G, B)=(255, 255, 255), (192, 192, 192), . . . , (64, 64, 64),and (0, 0, 0).

As explained above, in the present embodiment, in addition to theillumination intensity, the luminance in the incidence angle directionis set. Further, by using the illumination intensity and the luminancein the incidence angle direction, which are set, and the diffusereflection characteristic and the specular reflection characteristic ofthe printed material, which are measured in advance, the print luminanceperceived by a viewer is predicted. In addition, the example is shown inwhich the conversion characteristic is set so that “the slopes in thelinear areas of the output luminance become the same” in accordance withthe reproduction range of the predicted print luminance and “the lineararea for the luminance (saturation) of the input image increases”, andan image suitable to the viewing environment is generated.

In the embodiment described above, the conversion characteristic is setso that the linear area for the luminance of the input image increasesas the reproduction range of the predicted print luminance becomeslarger. Note that it may also be possible to predict the printsaturation from the tri-stimulus values PdX, PdY, and PdZ of the diffusereflection characteristic and the tri-stimulus values RdX, RdY, and RdZof the specular reflection characteristic, which are shown in FIG. 15.Then, it may also be possible to set the conversion characteristic sothat “the slopes in the linear areas of the output saturation become thesame” in a case where the reproduction range of the predicted printsaturation characteristic is different, and “the linear area for thesaturation of the input image increases”.

Fourth Embodiment

In the first and second embodiments described above, as described above,the example is shown in which the conversion characteristic of the imagedata is set so that “the slopes in the linear areas of the outputluminance become the same” and “the linear area for the luminance(saturation) of the input image increases”.

Further, in the third embodiment, in a case where the print luminance ispredicted, the luminance in the incidence angle is added as thecondition. Then, the example is shown in which the conversioncharacteristic of the image data is set so that “the slopes in thelinear areas of the output luminance become the same” in accordance withthe reproduction range of the print luminance and “the linear area forthe luminance of the input image increases”.

Note that, other than the illumination intensity and the luminance inthe incidence angle direction, there is a case where the visual densityof the printed material is changed. Here, as in FIG. 18, it isconsidered that a printed material is hung on the wall and the exhibitedprinted material (that is, the image printed on the printed material) isviewed. FIG. 18 shows a printed material (image) exhibited by theillumination of an illuminating apparatus having (a) a non-directionalillumination in the left field in the table and the printed material(image) exhibited by an illuminating apparatus having (b) a directionalillumination in the right field in the table.

In (a) in the left field in the table in FIG. 18, the image isirradiated by the non-directional illumination so that the illuminationintensity at the center portion of the image is 3,000 [lx] and each ofthe image portion and the background of the non-image portion (portionother than the image) is also irradiated by the illumination, andtherefore, the whole of the viewing environment becomes bright. That is,a luminance Cd_B1 of the background of the non-image portion becomesbright. The background of the non-image portion is shown as the areaother than the printed material (image) of the area of the wall on whichthe printed material (image) is hung. Further, in FIG. 18, although thearea to the right of the image portion is shown as the background of thenon-image portion, the area to the left of the image portion, the upperarea, or the lower area may be shown as the background of the non-imageportion. On the other hand, in (b) in the right field in the table inFIG. 18, the image is irradiated by the directional illumination so thatthe illumination intensity at the center of the image is 3,000 [lx] andonly the image portion is irradiated by the illumination, and therefore,a luminance Cd_B2 of the background of the non-image portion becomesdark.

As a supplement, it is assumed that the intensity of the illumination atthe center of the image is 3,000 [lx] and the luminance valuedistribution of the image portion is the same both in (a) in the leftfield in the table and in (b) in the right field in the table in FIG.18. That is, in a case where the luminance of the image portion alone ismeasured, the luminance of both the image portions indicates the samevalue.

Here, in a case where the image in (a) in the left field in the tableand the image in (b) in the right field in the table in FIG. 18 areviewed, in general, the image (b) in the right field in the table inFIG. 18 is more frequently perceived by a viewer as an image in whichthe portion from the halftone portion to the highlight portion of theprinted material is overexposed. That is, in a case where the printedmaterial is viewed under the directional illumination as in (b) in theright field in the table in FIG. 18, the printed material is viewed asif it were captured with the exposure being increased by a few stops.The reason is that the sense of sight of the viewer adapts to theluminance of the background of the non-image portion which is within thefield of view of the viewer in a case of viewing the image.

As regards this point, to be more detail, with (a) the non-directionalillumination in the left field in the table in FIG. 18, the backgroundluminance to which the sense of sight of the viewer adapts iscomparatively high. Because of this, compared to the luminance to whichthe sense of sight of the viewer has adapted, the luminance of thebrightest portion and the important color portion, such as the skin, ofthe image is unlikely to become so high. On the other hand, with (b) thedirectional illumination in the right field in the table in FIG. 18, thebackground luminance to which the sense of sight of the viewer adapts iscomparatively low. Because of this, as described above, the printedmaterial is viewed as if it were captured with the exposure beingincreased by a few stops and it is perceived that the portion from thehalftone portion to the highlight portion is overexposed.

The reason is that the contrast between the background luminance and theluminance of the brightest portion contributes to the change in thevisual density of the printed material (image). In the abovedescription, although the contrast between the background luminance andthe luminance of the brightest portion is taken, as the luminance of thebrightest portion, it may also be possible to take the luminance in aportion whose luminance is comparatively bright, such as the skinportion, or the luminance of the important color, such as the sky.

With these in mind, in a case where the difference between the luminanceof the image portion and the luminance of the background of thenon-image portion is large to a certain extent, suppression of thechange in the visual density perceived by a viewer is studied in thefollowing. FIG. 19 is a diagram showing the luminance of the brightestportion of the image in the exhibition environment (non-directionalillumination, directional illumination), the luminance of the backgroundof the non-image portion, and the luminance of the darkest portion ofthe image.

The left field in the table in FIG. 19 shows a luminance (maximum valueof print luminance predicted value Cd) Cd_Max1 of the brightest portionof the image, the luminance Cd_B1 of the background of the non-imageportion, and a luminance (print luminance minimum value) Cd_Min1 of thedarkest portion of the image in (a) a non-directional illuminationenvironment. Here, the contrast value of the luminance Cd_Max1 of thebrightest portion of the image to the luminance Cd_B1 of the backgroundof the non-image portion, that is, Cd_Max1/Cd_B1 is taken as C1.

Further, the center field in the table in FIG. 19 shows a luminance(maximum value of print luminance predicted value Cd) Cd_Max2 of thebrightest portion of the image, the luminance Cd_B2 of the background ofthe non-image portion, and a luminance (print luminance minimum value)Cd_Min2 of the darkest portion of the image in (b) a directionalillumination environment. Here, the contrast value of the luminanceCd_Max2 of the brightest portion of the image to the luminance Cd_B2 ofthe background of the non-image portion, that is, Cd_Max2/Cd_B2 is takenas C2.

Here, the illuminance at the image center is 3,000 [lx], and therefore,the luminance distribution of the image portion is the same in (a) inthe left field in the table in FIG. 19 and in (b) in the center field inthe table. That is, the luminance Cd_Max1 and the luminance Cd_Max2 ofthe brightest portion of the image indicate substantially the samevalue. Similarly, the luminance Cd_Min1 and the luminance Cd_Min2 of thedarkest portion of the image indicate substantially the same value.

Note that the luminance Cd_B1 and the luminance Cd_B2 of the backgroundof the non-image portion have a relationship of Cd_B1>Cd_B2, andtherefore, the luminance to which the sense of the sight of the vieweradapts is different between (a) in the left field in the table and (b)in the center field in the table in FIG. 19 and the image in (b) in thecenter field in the table in FIG. 19 is perceived as an image that isoverexposed. Further, in a case where the contrast value C1 in (a) inthe left field in the table in FIG. 19 and the contrast value C2 in (b)in the center field in the table in FIG. 19 are compared, C1<C2 willresult.

Consequently, in the present embodiment, as regards (a) in the leftfield in the table in FIG. 19 and (b) in the center field in the tablein FIG. 19, in order to make the same the visual impression of theimage, it is studied to make the same the contrast value C1 in (a) inthe left field in the table in FIG. 19 and the contrast value C2 in thecenter field in the table in FIG. 19. Specifically, in FIG. 19, it isstudied to change the luminance of the image so that the contrast of theluminance Cd_Max2 of the brightest portion of the image to the luminanceCd_B2 of the background of the non-image portion, that is,Cd_Max2/Cd_B2=C2 and the C1 become substantially the same.

Consequently, for example, by suppressing the luminance of the brightestportion of the image (that is, by reducing the illumination intensity ofthe illuminating apparatus) so that Cd_Max2 in (b) in the center fieldin the table in FIG. 19 becomes that as shown by Cd_Max2_e in (c) in theright field in the table in FIG. 19, it is possible to make the contrastvalue the same as the contrast value C1. Specifically, by reducing theluminance of the brightest portion of the image from Cd_Max2 toCd_Max2_e, it is possible to make a contrast value C3 of the luminanceCd_Max2_e of the brightest portion of the image to the luminance Cd_B2of the background of the non-image portion the same as the contrastvalue C1. That is, it is possible to change the luminance so that thevisual impression of the image is the same.

In FIG. 19, although Cd_Max1 and Cd_Max2 are explained as the luminance(print luminance maximum value) of the brightest portion of the image,it may also be possible to take the luminance in a portion whoseluminance is comparatively bright, such as the skin portion, or theluminance of the important color, such as the sky. Further, it is alsobe possible to use a value as the contrast value, which is obtained bysubtracting the luminance of the darkest portion of the image from theluminance of the brightest portion of the image and dividing thedifference by the luminance of the background of the non-image portion.That is, in a case where (Cd_Max1−Cd_Min1)/Cd_B1 is taken as C1 and(Cd_Max2_e−Cd_Min2)/Cd_B2 is taken as C3, it is also possible to changethe luminance of Cd_Max2_e so that C3 and C1 become the same. In eitherway, by changing the luminance of the brightest portion of the image sothat the contrast of the luminance of the brightest portion of the imageto the luminance of the background of the non-image portion is the same,it is possible to change the luminance so that the visual impression ofthe image is the same. In the following, the function (processing) tosuppress the change in the visual density perceived by a viewer isexplained specifically.

(Function Configuration of Image Processing Apparatus)

The functional configuration of the image processing apparatus accordingto the present embodiment is the same as that of the image processingapparatus according to the first embodiment, and is shown by the blockdiagram in FIG. 3. As in the first embodiment, the functions shown inFIG. 3 are implemented by supplying the programs for implementing thesefunctions to the image processing apparatus 100 shown in FIG. 2 andfurther, the image processing apparatus 100 executing the programs.Other than the viewing condition acquisition unit 204, the printluminance value prediction unit 207, the target luminance characteristicsetting unit 208, and the conversion characteristic setting unit 209,the functions thereof are the same as those of the image processingapparatus 100 of the first embodiment, and therefore, explanation isomitted here.

The viewing condition acquisition unit 204 acquires the viewingcondition set by a user by using a GUI shown in FIG. 20, to be describedlater. The print luminance value prediction unit 207 calculates(predicts) the luminance of the diffuse-reflected light of the printedmaterial in the viewing environment from the illumination intensityacquired by the viewing condition acquisition unit 204 and the printedmaterial reflection characteristic stored by the reflectioncharacteristic storage unit 206. The target luminance characteristicsetting unit 208 sets the target luminance characteristic to bereproduced as the printed material based on the background luminance(luminance of the background of the non-image portion) perceived by aviewer, which is acquired by the viewing condition acquiring unit 204,and the print luminance predicted by the print luminance valueprediction unit 207. The conversion characteristic setting unit 209 setsthe tone conversion characteristic for conversion in the tone conversionunit 210 based on the difference between the target luminancecharacteristic set by the target luminance characteristic setting unit208 and the print luminance predicted by the print luminance valueprediction unit 207.

(Viewing Condition Acquisition Unit)

Next, by using FIG. 20, a GUI provided by the viewing conditionacquisition unit 204 is explained. A user sets the viewing conditions byusing the GUI shown in FIG. 20. On the GUI shown in FIG. 20, a userselects “Candidate selection” in which the illumination intensity on aprinted material and the luminance of the background the non-imageportion are input intuitively and “Numerical value setting” in which theillumination intensity and the luminance of the background of thenon-image portion are input with a numerical value (physical value) bychecking a checkbox. As a supplement, the luminance of the background ofthe non-image portion in FIG. 20 is, for example, the luminance shown asCd−B1 and Cd_B2 in FIG. 18 as described above.

In a case where “Candidate selection” is selected, the illuminationintensity is selected from illumination intensity candidates, forexample, such as very bright (daytime outdoor), bright (illumination inart museum), moderate (office), and slightly dark (slightly dark office(ordinary home)). In addition, the luminance of the background of thenon-image portion is selected from candidates of the luminance of thebackground of the non-image portion, for example, such as very bright(white), bright (bright gray), moderate (gray), and dark (black).

Further, in a case where “Numerical value setting” is selected, asregards the illumination intensity, the illumination intensity (value ofilluminance lux (Lx)) on the printed material is input in the text box,or a specific illumination intensity is selected by moving a slider barto the left or right. In addition, also as regards the backgroundluminance of the non-image portion, similarly, the luminance of thebackground of the non-image portion perceived by a viewer is input asthe luminance value [cd/m²] or a specific luminance of the background ofthe non-image portion is selected by moving the slider bar to the leftand right. To the candidate selected as “Candidate selection”, theilluminance lux corresponding to the candidate is set, and for example,in a case where moderate (office) is selected as the illuminationintensity, the subsequent processing is performed by regarding that 800[lx] is selected. Further, similarly, in a case where moderate (gray) isselected as the luminance of the background of the non-image portion,the subsequent processing is performed by regarding that 50 [cd/m²] isselected.

In the embodiment described above, although explanation is given byusing the illuminance [lx] as the illumination intensity (luminance),the illumination luminance is not necessarily limited to this, and forexample, it may also be possible to use the luminance [cd/m²] and [nit].In addition, it may also be possible to cause a user to select thenon-directional illumination or the directional illumination as theilluminating apparatus. In that case, it may also be possible to performthe setting so that, for example, on a condition that the non-directedillumination is selected, the luminance of the background of thenon-image portion is made comparatively high (bright (bright gray)), andon a condition that the directional illumination is selected, theluminance of the background of the non-image portion is madecomparatively low (dark (black)). In addition, in order to cause theillumination intensity to be input more accurately, it may also bepossible to display a note to the effect that the illuminancemeasurement by an illuminometer on the printed material that is posted,and the measurement of the luminance of the background of the non-imageportion are necessary on the GUI.

(Image Processing)

Next, by using FIG. 8, the image processing in the image processingapparatus 100 is explained. As described above, FIG. 8 is the flowchartshowing the procedure of the image processing in the image processingapparatus 100. The processing at step S501 and step S508 is the same asthat in the first embodiment, and therefore, explanation thereof isomitted here.

In a case where the image data input by the luminance calculation unit203 is converted into the input image data whose luminance is linear,the viewing condition acquisition unit 204 acquires the viewingconditions (the illumination intensity Lt [Lx [lx], the luminance Cd_B[cd/m²] of the background of the non-image portion) selected by a user(S502). As a supplement, the luminance of the background of thenon-image portion is, for example, the luminance shown as Cd_B1 andCd_B2 in FIG. 18 as described above.

In a case where the viewing conditions are acquired by the viewingcondition acquisition unit 204 (S502), the print luminance valueprediction unit 207 acquires the diffuse reflection characteristic (Pd)from the reflection characteristic storage unit 206 (S503). The printluminance value prediction unit 207 calculates the luminance Cd of thediffuse-reflected light of the printed material based on the viewingcondition (the illumination intensity Lt [lx]) and the diffusereflection characteristic (Pd), which are acquired (S504).

The luminance Cd of the diffuse-reflected light of the printed materialis calculated by the following formula.

Cd=Pdy/100×Lt/π[cd/m ²]  (7)

Here, π indicates the ratio of the circumference of a circle to itsdiameter and PdY indicates the Y component in the tri-stimulus valuesXYZ of the diffuse reflection characteristic, and PdY has a rangebetween 0.77 and 90.3 as in FIG. 5 of the first embodiment.

The print luminance value prediction unit 207 determines whether or notthe luminance Cd of the diffuse-reflected light has been calculated forall the patches (S505). Then, in a case where it is determined that thecalculation of the luminance Cd of the diffuse-reflected light has notbeen completed for all the patches (No at S505), the image processingapparatus 100 returns the processing to S504 and calculates theluminance Cd of the diffuse-reflected light for all the patches.

As described above, in the present embodiment, for the input RGB image(image whose luminance is linear) obtained by equally dividing the grayline into five portions, the diffuse reflection characteristic relatingto each piece of image data is acquired. That is, the printed materialreflection characteristic relating to each piece of image data isacquired for the five patches of the input images whose luminance islinear (R, G, B)=(255, 255, 255), (192, 192, 192), (128, 128, 128), (64,64, 64), and (0, 0, 0).

The target luminance characteristic setting unit 208 sets the targetluminance characteristic to be reproduced as the printed material basedon the luminance Cd of the diffuse-reflected light of the printedmaterial, which is calculated by the print luminance value predictionunit 207 and the luminance Cd_B of the background of the non-imageportion, which is acquired by the viewing condition acquisition unit 204(S506).

In the present embodiment, before setting the target luminancecharacteristic T_Cd, a tentative target luminance characteristic I_Cd isset. Here, the tentative target luminance characteristic I_Cd is thesame as the target luminance characteristic T_Cd in the firstembodiment. That is, the tentative target luminance characteristic I_Cdis set so that in a case where the reproduction range of the printluminance characteristic is different, the slope in the linear area ofthe output luminance in a case where the reproduction range isrelatively small and the slope in the linear area of the outputluminance in a case where the reproduction range is relatively largebecome the same.

Further, the setting method of the tentative target luminancecharacteristic I_Cd is also the same as the setting method of the targetluminance characteristic T_Cd described above at step S506 of the firstembodiment. That is, as shown in FIG. 22, the tentative target luminancecharacteristic I_Cd is calculated from the two different tables (Tbl_1,Tbl_2) prepared in advance and the function of the weighting a value inaccordance with the maximum value Cd_Max [cd/m²] of the print luminancepredicted value Cd.

Further, here, the maximum value Cd_Max of the print luminance predictedvalue (luminance of the diffuse-reflected light of the printed material)Cd is also calculated based on formula (7) as in the first embodiment.Consequently, for example, in a case where the illumination intensity inFIG. 19 is 3,000 [Ix], the maximum value Cd_Max of the print luminancepredicted value Cd is calculated as about 1,000 [cd/m²].

In the following, the setting method of the tentative target luminancecharacteristic I_Cd according to the present embodiment is explainedsupplementally by using FIG. 21. As described above, FIG. 21 shows theprint illuminance predicted value Cd of a patch, which is predicted inaccordance with the illumination intensity, and the tentative targetluminance characteristic I_Cd set based on the print luminance predictedvalue.

As in the first embodiment, the tentative target luminancecharacteristic I_Cd in a case where the illumination intensity is normal(300 [Ix]) has the linear characteristic in the portion from the shadowportion to the halftone portion (area in which the input pixel value isless than 64 (6005)). Further, in the portion from the halftone portionto the highlight portion (area in which the input pixel value is greaterthan 64 (6005)), the conversion characteristic bends and has thenonlinear characteristic (6003). On the other hand, the tentative targetilluminance characteristic I_Cd in a case where the illuminationintensity is high (3,000 [lx]) has the linear characteristic in theportion from the shadow portion to the highlight portion (6004).

In this case, the tentative target luminance characteristic I_Cd that isset in the target luminance characteristic setting unit 208 iscalculated based on the following formula as in the first embodiment.

I_Cd(ln)=(1−α(Cd_Max))×Tbl_1(In)+α(Cd_Max)×Tbl_2(In)   (8)

In is the input pixel value (0≤In≤255). Further, Tbl_1 (In) is theluminance value of Tbl_1 in the input pixel value In and Tbl_2 (In) isthe luminance value of Tbl_2 in the input pixel value In. Then, thetentative target luminance characteristic I_Cd calculated by the aboveformula in a case where the weighting a value is varied as α=0.00(7004), α=0.33 (7005), α=0.66 (7006), and α=1.00 (7007) is shown on thelower side in FIG. 22. By referring to FIG. 22, it is known that thesetting is performed so that in a case where the reproduction range ofthe print luminance characteristic is different, the slope in the lineararea of the output luminance in a case where the reproduction range isrelatively small and the slope in the linear area of the outputluminance in a case where the reproduction range is relatively largebecome the same. That is, it is known that the tentative targetluminance characteristic I_Cd is the same as the target luminancecharacteristic T_Cd of the first embodiment. As a supplement, in thiscase, as explained in the second embodiment, it may also be possible toset the target luminance characteristic so that the larger thereproduction range of the predicted print luminance characteristicbecomes, the more the linear area increases.

Then, after the tentative target luminance characteristic I_Cd iscalculated as described above, next, the target luminance characteristicT_Cd to be reproduced as the printed material is set (calculated) basedon the background luminance Cd_B [cd/m²]. In the present embodiment, itis assumed that the background luminance Cd_B in a predeterminedenvironment, the luminance of the brightest portion of the image (theprint luminance maximum value) Cd_Max, and the contrast value are storedin advance as a reference target in a case where the target luminancecharacteristic T_Cd is set. For example, in the a where thepredetermined environment is taken as the environment of thenon-directional illumination shown in (a) in the left field in the tablein FIG. 19, the background luminance Cd_B1, the luminance of thebrightest portion of the image (the print luminance maximum value)Cd_Max1, and the contrast value Cl=Cd_Max1/Cd_B1 are stored as areference target.

Here, the target luminance characteristic T_Cd to be reproduced as theprinted material (specifically, the target luminance characteristic T_Cdin the environment of the illuminating apparatus having the directionalillumination in FIG. 19) is calculated by the following formula. Morespecifically, the target luminance characteristic T_Cd to be reproducedas the printed material is calculated by the following formula based onthe illumination intensity Lt [lx](3,000 [lx] in (b) in the center fieldin the table in FIG. 19) and the background luminance Cd_B [cd/m²](Cd_B2 [cd/m²] in (b) in the center field in the table in FIG. 19).

T_Cd=I_Cd×C1/C  (9)

In the above formula (9), I_Cd is the tentative target luminancecharacteristic in the calculation-target environment (specifically, theenvironment in (b) in the center field in the table in FIG. 19).Further, C1 is the contrast value in the predetermined environment(specifically, in the environment in (a) in the left field in the tablein FIG. 19), which is taken as a reference target (reference).Furthermore, C is the contrast value in the calculation-targetenvironment of the target luminance characteristic T_Cd and in thepresent embodiment, is expressed by the following formula as a ratio ofthe print luminance maximum value Cd_Max to the background luminanceCd_B.

C=Cd_Max/Cd_B  (10)

That is, in the environment in (b) in the center field in the table inFIG. 19, the contrast value C is expressed as C=Cd_Max2/Cd_B2 based onthe above formula.

As described above (that is, as expressed in the above formula (9)), ina case where the contrast value C in the calculation-target environmentis great compared to the contrast value C1, which is taken as thereference, the target luminance characteristic T_Cd is set small. On theother hand, in a case where the contrast value C in thecalculation-target environment is small compared to the contrast valueC1, which is taken as the reference, the target luminance characteristicT_Cd is set great. That is, the target luminance characteristic T_Cd isset so that the contrast value C and the contrast value C1, which istaken as the reference, become the same.

Here, the reason the target luminance characteristic T_Cd is set asexpressed by the above formula is to, as described above, suppress achange in visual density perceived by a viewer by making the contrastvalue the same as the contrast value in the predetermined environment,which is taken as the reference.

In the above description, although explanation is given by defining thecontrast as the ratio of the luminance of the brightest portion of theimage to the luminance of the background of the non-image portion, thecontrast is not necessarily limited to this. Consequently, for example,it may also be possible to calculate the target luminance characteristicT_Cd so that the contrast values become the same by using the luminancein a portion where luminance is comparatively bright, such as the skinportion, or the luminance of the important color, such as the sky inplace of the luminance of the brightest portion of the image (printluminance maximum value).

Further, it may also be possible to use a value as the contrast value,which is obtained by subtracting the luminance of the darkest portion ofthe image from the luminance of the brightest portion of the image anddividing the difference by the luminance of the background of thenon-image portion. That is, it may be possible to take the contrastvalue C as C=(Cd_Max−Cd_Min)/Cd_B. In addition, it may also be possibleto perform the logarithmic operation, such as C=Log (Cd_Max/Cd_B) forthe contrast value C, or perform the exponential operation, such asC=(Cd_Max/Cd_B){circumflex over ( )}n (n is a real number) for thecontrast value C. In either case, by changing the target luminancecharacteristic T_Cd so that the contrast value of the luminance of thebrightest portion of the image to the luminance of the background of thenon-image portion is the same, it is possible to suppress a change invisual density perceived by a viewer. That is, it is possible to makethe visual impression of the image substantially the same.

In addition, in the present embodiment, the example is shown in whichthe tentative target luminance characteristic I_Cd is set so that theslopes in the linear areas of the output luminance become the same evenin a case where the reproduction range of the print luminancecharacteristic is different by using the two different tables. Note thatthe setting of the tentative target luminance characteristic I_Cd is notnecessarily limited to the method described above and for example, itmay also be possible to define the target luminance characteristic T_Cdby a spline function and set the curve of the spline function so thatthe slopes in the linear areas of the output luminance become the same.

Here, returning to FIG. 8, the conversion characteristic setting unit209 sets the conversion characteristic Out_Tb1 by using the printluminance predicted value Cd of the patch, which is predicted by theprint luminance value prediction unit 207, and the target luminancecharacteristic T_Cd set by the target luminance characteristic settingunit 208 (S507). As in the first embodiment, the conversioncharacteristic Out_Tbl is set so that the print luminance predictedvalue Cd becomes the target luminance characteristic T_Cd. Theprocessing to set the conversion characteristic Out_Tbl is the same asthat of the first embodiment, and therefore, here, explanation thereofis omitted.

As above, in the present embodiment, the example is shown in which it ispossible to suppress a change in visual density perceived by a viewer,which results from that the luminance of the background of the non-imageportion is different (that is, the contrast is different).

Fifth Embodiment

In the above-described embodiments, the example is shown in which theconversion characteristic of image data is set so that “the slopes inthe linear areas of the output luminance (saturation) become the same”in accordance with the reproduction range of the print luminance(saturation) predicted from the illumination intensity. Further, at thesame time, the example is shown in which the conversion characteristicof image data is set so that “the linear area for the luminance(saturation) of the input image increases” in accordance with thereproduction range of the print luminance (saturation) predicted fromthe illumination intensity.

Note that the conversion characteristic setting target is notnecessarily limited to the tone conversion characteristic in the toneconversion unit 210. Consequently, for example, it may also be possiblefor the print processing unit 211 shown in FIG. 6 described above to set(control) one or all of the CMS processing unit 401, the colorseparation unit 402, and the halftone processing unit 403.

In this case, it is sufficient for the CMS processing unit 401 to changeor set the color profile 404. Further, it is sufficient for the colorseparation processing unit 402 to change or set the color separationtable 405. Furthermore, it is sufficient for the halftone processingunit 403 to change or set the halftone parameter 406. In either case, itis only required for the conversion characteristic of image data to beset so that “the slopes in the linear areas of the output luminance(saturation) become the same” in accordance with the reproduction rangeof the predicted print luminance (saturation), and in addition to that,“the linear area for the luminance (saturation) increases”.

OTHER EMBODIMENTS

Embodiment(s) of the present invention can also be realized by acomputer of a system or apparatus that reads out and executes computerexecutable instructions (e.g., one or more programs) recorded on astorage medium (which may also be referred to more fully as a‘non-transitory computer-readable storage medium’) to perform thefunctions of one or more of the above-described embodiment(s) and/orthat includes one or more circuits (e.g., application specificintegrated circuit (ASIC)) for performing the functions of one or moreof the above-described embodiment(s), and by a method performed by thecomputer of the system or apparatus by, for example, reading out andexecuting the computer executable instructions from the storage mediumto perform the functions of one or more of the above-describedembodiment(s) and/or controlling the one or more circuits to perform thefunctions of one or more of the above-described embodiment(s). Thecomputer may comprise one or more processors (e.g., central processingunit (CPU), micro processing unit (MPU)) and may include a network ofseparate computers or separate processors to read out and execute thecomputer executable instructions. The computer executable instructionsmay be provided to the computer, for example, from a network or thestorage medium. The storage medium may include, for example, one or moreof a hard disk, a random-access memory (RAM), a read only memory (ROM),a storage of distributed computing systems, an optical disk (such as acompact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™),a flash memory device, a memory card, and the like.

According to the present embodiment, it is possible to generate an imagein which a visual change depending on the viewing environment issuppressed.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

1. An image processing apparatus that generates, in accordance withintensity of light with which an image printed based on input image datais irradiated, print image data on the image from the input image data,the image processing apparatus comprising: an acquisition unitconfigured to acquire a viewing condition under which the image isviewed; a prediction unit configured to predict a print luminancecharacteristic corresponding to print image data on the image based onthe viewing condition and a reflection characteristic corresponding toprint image data on the image; a derivation unit configured to derive atarget luminance characteristic under the viewing condition based on theprint luminance characteristic; a setting unit configured to set a toneconversion characteristic that converts the input image data into printimage data on the image based on the print luminance characteristic andthe target luminance characteristic; and a generation unit configured togenerate output image data on the image by converting the input imagedata by using the tone conversion characteristic, wherein the derivationunit drives, in a case where a reproduction range of an illuminationintensity in the print luminance characteristic is different, the targetluminance characteristic so that a linear area of an output luminance ina case where the reproduction range is relatively large is larger than alinear area of an output luminance in a case where the reproductionrange is relatively small.
 2. The image processing apparatus accordingto claim 1, wherein the derivation unit derives, in a case where areproduction range of an illumination intensity in the print luminancecharacteristic is different, the target luminance characteristic so thata slope in a linear area of an output luminance in a case where thereproduction range is relatively small and a slope in a linear area ofan output luminance in a case where the reproduction range is relativelylarge become the same.
 3. The image processing apparatus according toclaim 1, wherein the acquisition unit acquires at least an illuminationintensity with which the image is irradiated as the viewing conditionand the prediction unit predicts the reflection characteristic based onat least a diffuse reflection characteristic.
 4. The image processingapparatus according to claim 3, wherein the acquisition unit furtheracquires a luminance in a light incidence angle direction facing apositional relationship between a viewing position and the image as theviewing condition and the prediction unit further predicts thereflection characteristic based on a specular reflection characteristic.5. The image processing apparatus according to claim 4, wherein in thereflection characteristic, a number of values of diffuse reflectancepossessed as the diffuse reflection characteristic and a number ofvalues of specular reflectance possessed as the specular reflectioncharacteristic are different.
 6. The image processing apparatusaccording to claim 4, wherein the diffuse reflection characteristic ismeasured by a spectrophotometer and the specular reflectioncharacteristic is measured by a variable angle measuring unit.
 7. Theimage processing apparatus according to claim 3, wherein the acquisitionunit further acquires a background luminance of a portion other than theimage, which is perceived by a viewer, as the viewing condition and thederivation unit further derives a contrast value of a luminance of abrightest portion of the image to the background luminance in a casewhere the image is irradiated with a directional illumination andderives the target luminance characteristic based on the print luminancecharacteristic and the contrast value.
 8. The image processing apparatusaccording to claim 7, wherein the derivation unit derives the targetluminance characteristic so that the contrast value and a contrast valueof a luminance of a brightest portion of the image to the backgroundluminance in a case where a center part of the image is irradiated witha non-directional illumination whose illumination intensity is equal toan illumination intensity with which a center part of the image isirradiated at the time of derivation of the contrast value becomesubstantially the same.
 9. The image processing apparatus according toclaim 4, wherein the illumination intensity, or the illuminationintensity and a luminance in the incidence angle direction are set by auser.
 10. The image processing apparatus according to claim 7, whereinthe illumination intensity, or the illumination intensity and abackground luminance of a portion other than the image are set by auser.
 11. The image processing apparatus according to claim 1, whereinin the input image data, a pixel value and a scene luminance are in aliner relationship.
 12. An image processing apparatus that generates, inaccordance with intensity of light with which an image printed based oninput image data is irradiated, print image data on the image from theinput image data, the image processing apparatus comprising: anacquisition unit configured to acquire a viewing condition under whichthe image is viewed; a prediction unit configured to predict a printsaturation characteristic corresponding to print image data on the imagebased on the viewing condition and a reflection characteristiccorresponding to print image data on the image; a derivation unitconfigured to derive a target saturation characteristic under theviewing condition based on the print saturation characteristic; asetting unit configured to set a tone conversion characteristic thatconverts the input image data into print image data on the image basedon the print saturation characteristic and the target saturationcharacteristic; and a generation unit configured to generate print imagedata on the image by converting the input image data by using the toneconversion characteristic, wherein the derivation unit drives, in a casewhere a reproduction range of an illumination intensity in the printsaturation characteristic is different, the target saturationcharacteristic so that a linear area of an output saturation in a casewhere the reproduction range is relatively large is larger than a lineararea of an output saturation in a case where the reproduction range isrelatively small.
 13. An image forming apparatus comprising: the imageprocessing apparatus according to claim 1; and an output unit configuredto output the print image data generated by the image processingapparatus.
 14. A non-transitory computer readable storage medium storinga program for causing a computer to function as an image processingapparatus that generates, in accordance with intensity of light withwhich an image printed based on input image data is irradiated, printimage data on the image from the input image data, where the imageprocessing apparatus comprises: an acquisition unit configured toacquire a viewing condition under which the image is viewed; aprediction unit configured to predict a print luminance characteristiccorresponding to print image data on the image based on the viewingcondition and a reflection characteristic corresponding to print imagedata on the image; a derivation unit configured to derive a targetluminance characteristic under the viewing condition based on the printluminance characteristic; a setting unit configured to set a toneconversion characteristic that converts the input image data into printimage data on the image based on the print luminance characteristic andthe target luminance characteristic; and a generation unit configured togenerate output image data on the image by converting the input imagedata by using the tone conversion characteristic, wherein the derivationunit drives, in a case where a reproduction range of an illuminationintensity in the print luminance characteristic is different, the targetluminance characteristic so that a linear area of an output luminance ina case where the reproduction range is relatively large is larger than alinear area of an output luminance in a case where the reproductionrange is relatively small.
 15. An image processing method of generating,in accordance with intensity of light with which an image printed basedon input image data is irradiated, print image data on the image fromthe input image data, the image processing method comprising: anacquisition step of acquiring a viewing condition under which the imageis viewed; a prediction step of predicting a print luminancecharacteristic corresponding to print image data on the image based onthe viewing condition and a reflection characteristic corresponding toprint image data on the image; a derivation step of deriving a targetluminance characteristic under the viewing condition based on the printluminance characteristic; a setting step of setting a tone conversioncharacteristic that converts the input image data into print image dataon the image based on the print luminance characteristic and the targetluminance characteristic; and a generation step of generating printimage data on the image by converting the input image data by using thetone conversion characteristic, wherein at the derivation step, in acase where a reproduction range of an illumination intensity in theprint luminance characteristic is different, the target luminancecharacteristic is derived so that a linear area of an output luminancein a case where the reproduction range is relatively large is largerthan a linear area of an output luminance in a case where thereproduction range is relatively small.
 16. The image processing methodaccording to claim 15, wherein at the derivation step, in a case where areproduction range of an illumination intensity in the print luminancecharacteristic is different, the target luminance characteristic isderived so that a slope in a linear area of an output luminance in acase where the reproduction range is relatively small and a slope in alinear area of an output luminance in a case where the reproductionrange is relatively large become the same.
 17. The image processingmethod according to claim 15, wherein at the acquisition step, at leastan illumination intensity with which the image is irradiated is acquiredas the viewing condition and at the prediction step, the reflectioncharacteristic is predicted based on at least a diffuse reflectioncharacteristic.
 18. The image processing method according to claim 17,wherein at the acquisition step, a luminance in a light incidence angledirection facing a positional relationship between a viewing positionand the image is further acquired as the viewing condition and at theprediction step, the reflection characteristic is further predictedbased on a specular reflection characteristic.
 19. The image processingmethod according to claim 18, wherein in the reflection characteristic,a number of values of diffuse reflectance possessed as the diffusereflection characteristic and a number of values of specular reflectancepossessed as the specular reflection characteristic are different. 20.The image processing method according to claim 18, wherein the diffusereflection characteristic is measured by a spectrophotometer and thespecular reflection characteristic is measured by a variable anglemeasuring unit.